It has become the norm that communications are performed with multiple frequency bands in various areas in a mobile communication system. There are plans to further increase available frequency bands. Radio circuits incorporated into mobile terminals in such a system have frequency characteristics and therefore different circuits adjusted to different frequencies are required, causing concern that circuit sizes may become bulky. To avoid bulky circuit sizes, Japanese Patent No. 4464919, for example, describes an approach to supporting multiple bands by providing switches and matching elements in a matching circuit and turning on and off the switches to change impedance in the matching circuit.
For the variable matching circuit described in Japanese Patent No. 4464919 to operate at N bands, a line stub SB1 that functions as a matching element is connected to a line L11 and, in addition, N−1 line stubs SB2 to SBN functioning as matching elements need to be connected to N−1 lines L12 to UN through N−1 switches SW1 to SWN−1 as illustrated in FIG. 19. For example, for the matching circuit to operate at two bands, one switch (SW1) and two matching elements (SB1, SB2) are required; for the matching circuit to operate at three bands, two switches (SW1, SW2) and three matching elements (SB1, SB2, SB3) are required. For example, for using a power amplifier at three bands, two switches and three matching elements are required in each of the matching circuits on the input and output ends of the power amplifier. Basically, one switch and one matching element are used to achieve matching at one desired frequency band. This approach has an advantage that a matching state at different frequencies can be adjusted independently of one another because matching at a frequency band does not affect matching at another frequency band when the switch is off. However, as the number of frequency bands that need to be supported increases, the number of required switches and the number of matching elements increase proportionally, causing to expand the required circuit mounting area.